On Wed, 21 Aug 2002, Roman Black wrote:
>
> Actually it is. You store the new pins in an XORed
> form. :o) But there is a problem that your code below
> still takes 9 cycles (once goto is included).

<snip>

Maybe I don't follow. This is what I meant:

pwm_loop

                                ; first output current1 to motor
        movf current1,w         ; get currents and phase switching
        movwf PORTB             ; send to motor!

        movf  diff,w            ;
        xorwf inputs_last       ;

        ;-------------------------
                                ; now output current2
        movf current2,w         ;
        movwf PORTB             ; send to motor!

;        nop                     ; let ports settle
;        nop                     ; + some delay

        movf  inputs_last,w     ; now test input pins
        xorwf PORTA,w
        movwf diff

        skpnz
         goto pwm_loop          ; z, inputs not changed, so keep looping
        ;-------------------------------------------------

That has the 4/8 cycle requirement.  There's a trick to squeeze in another
instruction and still meet the timing. It's probably obvious, so I won't
bother mentioning it. :)

Scott

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